Download Module 1: CRRT Overview

Module 1: CRRT Overview
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Module 1: CRRT Overview
CRRT OVERVIEW
TABLE OF CONTENTS
Lesson 1. Renal Anatomy & Physiology
Lesson 2. Acute Renal Failure
Lesson 3. What is CRRT?
Lesson 4. Delivery of CRRT
Lesson 5. CRRT Considerations
These materials were created by Baxter Healthcare Corporation and Edwards Lifesciences Corporation
as part of the Critical Care Nephrology Alliance. Seeking to provide CRRT professionals with the
highest caliber of multidisciplinary expertise, products and services, the Alliance brings together
the unique strengths of Baxter, an expert in renal therapies, and Edwards Lifesciences Corporation,
a leader in critical care.
Notes:
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Module 1: Learning Objectives
LEARNING OBJECTIVES
•
Recognize the role of the kidney in maintaining balance
in the body
•
Understand the causes and phases of acute renal
failure (ARF)
•
Understand the principles of fluid and solute
management in continuous renal replacement therapy
(CRRT): diffusion, convection, adsorption, ultrafiltration
•
Understand the rationale for using each CRRT modality
- Slow continuous ultrafiltration (SCUF)
- Continuous veno-venous hemofiltration (CVVH)
- Continuous veno-venous hemodialysis (CVVHD)
- Continuous veno-venous hemodiafiltration (CVVHDF)
•
Discuss the importance of vascular access and
anticoagulation in successful CRRT usage
•
Understand the rationale for using substitution and
dialysate fluids in CRRT
•
Recognize all the components needed to perform a
successful CRRT treatment
•
Recognize advantages, limitations and special
requirements when performing CRRT
Notes:
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Lesson 1: Renal Anatomy and Physiology
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Module 1: Lesson 1: Renal Anatomy and Physiology
RENAL ANATOMY AND PHYSIOLOGY
Every time the heart beats, 25% of the cardiac output is sent to the kidneys.
THE KIDNEY
•
The kidney functions using three principles: ultrafiltration, excretion and reabsorption
•
The kidney consists of three parts:
Cortex
Medulla
Renal Pelvis
Notes:
Module 1: Lesson 1: Renal Anatomy and Physiology
COMPONENTS OF THE KIDNEY
1. The cortex (outer layer) contains 80% of the nephrons. These nephrons filter the blood
continuously to maintain balance.
2. The medulla (inner layer) contains 20% of the nephrons. These nephrons also filter the blood,
but have the added responsibility to concentrate urine. This becomes an important diagnostic
tool.
3. The renal pelvis is the start of the collecting system, containing the collecting tubules and the
ureter.
Additionally, ureters carry urine into the bladder where it is stored until it is eliminated from the
body through the urethra.
RESIDUAL KIDNEY FUNCTION
Notes:
•
The kidney is capable of maintaining the body’s
equilibrium until about 50% of the nephrons are
damaged
•
After 50% loss of kidney function, the body begins to
make trade-offs to maintain homeostasis. For
example, parathyroid hormone (PTH) increases to
compensate for increased excretion of phosphorus.
The patient will likely remain asymptomatic
•
After 90% loss of kidney function, some form of renal
replacement therapy is necessary to preserve life
Module 1: Lesson 1: Renal Anatomy and Physiology
Glomerulus
THE NEPHRON
The functional unit of the kidney is
called a nephron. Each kidney has
about one million nephrons. Each
nephron contains a glomerulus, which
functions as an individual filtering unit.
It also contains tubules for secretion
and absorption of substances.
Tubules
THE BLOOD PATHWAYS
Blood leaves the heart, enters the abdominal aorta and enters the kidney through the renal artery.
The renal artery divides into seven branches of arterioles until it becomes the afferent arteriole.
The afferent arteriole carries blood to the glomerulus, where it is filtered. It then leaves the
glomerulus through the efferent arteriole, and is returned to the venous system. This system
branches into many larger vessels until it becomes the renal vein.
Blood leaves the kidney via the renal vein, and is returned to the heart via the inferior vena cava.
Notes:
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Module 1: Lesson 1: Renal Anatomy and Physiology
THE GLOMERULUS
The glomerulus consists of a group of cells with selective
permeability. It is a semi-permeable membrane.
Selective permeability means that certain substances will
cross the membrane and others will not be allowed to cross.
Through selective permeability, the kidney regulates fluid and
electrolyte balance. The tea filter is a sample of a membrane
with selective permeability.
The kidneys produce approximately 180 liters of filtrate per
day. Only 1.5 - 2 liters are excreted as urine. The remaining
178 liters remain in the body. This is simply recycled body
water.
THE AFFERENT AND EFFERENT ARTERIOLES
The afferent arteriole has a larger lumen than the efferent arteriole. Therefore, blood flows into the
glomerulus faster than it flows out, which creates a pooling of blood in the Bowman’s capsule.
Hydrostatic pressure on the blood will force fluid to cross the glomerular membrane and enter the
tubules. This is ultrafiltration.
As filtrate flows through the tubular network, special cells will respond to the need for
reabsorption and secretion.
Notes:
Module 1: Lesson 1: Renal Anatomy and Physiology 11
The end product of this filtrate is urine. In the normal
kidney, this urine will be the right color, have the right
osmolality and contain the right substances.
The urine color is light to dark yellow depending on
volume, and the color is provided by solutes.
Osmolality is used because it measures particles
independently of their molecular weight. Substances
including urea, creatinine, phosphorus, potassium
acids etc. are cleaned and filtered to keep the blood
values normal.
The goal of the kidney is to maintain a normal
balance of fluids, electrolytes, minerals and acidbase. It works continuously to preserve equilibrium
and homeostasis.
The kidneys also produce hormones like renin,
vitamin D and erythropoietin. Renin promotes
sodium retention and it also causes vasoconstriction.
Vitamin D stimulates calcium and phosphate
absorption. Erythropoietin promotes production of
red blood cells in the bone marrow.
Notes:
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Module 1: Lesson 1: Renal Anatomy and Physiology
In summary:
• With every heartbeat, 25% of the cardiac output goes to the kidneys
• Blood enters the abdominal aorta and flows into the renal artery
• The renal artery branches until it becomes the afferent (entering) arteriole
• The afferent arteriole takes the blood into the glomerulus (the filtering unit located in
Bowman’s capsule of the nephron)
- Because blood flows into Bowman’s capsule faster than it flows out, a resulting increase
in pressure facilitates filtration
• The efferent (leaving) arteriole takes the blood coming out of the glomerulus and returns it to
the venous system. The venous system branches into larger vessels to become the renal
vein
• The renal vein carries blood to the vena cava and returns it to the heart
• This process is continuous
Notes:
Module 1: Lesson 1: Renal Anatomy and Physiology 13
KIDNEY FUNCTIONS
The kidney has several functions (CRRT deals with the first four functions):
1. Fluid balance
- Through ultrafiltration and reabsorption
2. Electrolyte balance
- Through reabsorption and excretion
3. Acid-base balance
- Through reabsorption and excretion
4. Excretion of drugs and by-products of metabolism
- Nitrogen
- Urea
- Creatinine
5. Synthesis of erythropoietin
- Stimulates the bone marrow to produce healthy red blood cells and help them mature
6. Regulation of blood pressure
- Secretes renin to help regulate blood pressure
7. Maintenance of calcium:phosphorus balance
- A normal ratio is 2:1
- The kidneys produce the active vitamin D and regulate calcium
- The kidney also is the major excretor of phosphorus. If the kidney does not function
properly, phosphorus builds up in the blood stream. As the body struggles to maintain
the 2:1 calcium:phosphorus ratio, it will steal calcium from the bones by increasing
parathyroid hormone (PTH) production
Notes:
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Module 1: Lesson 1: Renal Anatomy and Physiology
KIDNEY FACTS
•
The kidneys are two bean shaped organs, located just below the inferior boundary of the rib
cage
•
Each kidney can function independently
of the other
•
Each kidney weighs approximately 110 – 170
grams and is about the size of a human
fist
•
The kidneys receive 1,200 milliliters of blood
(25% of cardiac output) every minute. That is
72 liters per hour or 1,728 liters per day
•
Normal kidney function is measured in terms
of glomerular filtration rate (GFR). Normal GFR
is 125 milliliters per minute. That is 7,500
milliliters per hour or 180 liters per day
Notes:
Module 1: Lesson 1: Renal Anatomy and Physiology 15
•
The kidney is divided into three parts: the cortex, the medulla and the renal pelvis
•
The functional unit of the kidney is called a nephron
•
Each kidney contains approximately one million nephrons
•
Each nephron has a glomerulus, which functions as an individual filtering unit. It also contains
the tubules which are responsible for reabsorption and secretion
•
The kidney will maintain homeostasis in the body until less than 50% of the nephrons are
functioning
•
The kidney has several roles:
- Fluid balance
- Electrolyte balance
- Acid-base balance
- Excretion of drugs and by-products of metabolism
- Synthesis of erythropoietin
- Regulation of blood pressure
- Maintenance of calcium:phosphorus balance
Notes:
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Lesson 2: Acute Renal Failure
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Module 1: Lesson 2: Acute Renal Failure
ACUTE RENAL FAILURE / ACUTE RENAL INJURY
Acute renal failure (ARF) results from the sudden loss
of kidney function. Acute renal failure in the setting of
critical care patients is defined as an abrupt decline
in glomerular filtration rate resulting from ischemic or
toxic injury to the kidney.1
•
•
•
•
Waste products that are usually excreted by the
kidney accumulate in the blood
ARF may be accompanied by metabolic,
acid-base and electrolyte disturbances and fluid
overload
ARF may affect many other organ systems
ARF often requires immediate treatment
Notes:
1
AR Nissenson: Acute Renal Failure: Definition and pathogenesis. Kidney Int Suppl. 1998 May; 66:S7-10
19
20
Module 1: Lesson 2: Acute Renal Failure
Acute renal failure can be classified as:
A.
PRE-RENAL
Pre-renal failure typically results from decreased
blood flow to the kidneys. The reduction in
glomerular filtration enables the solutes in the
blood to accumulate but does not cause any
structural damage to the kidney itself. Examples
of situations leading to pre-renal failure may
include dehydration, hemorrhage, congestive
heart failure, sepsis, and embolism/thrombosis.
B.
RENAL (INTRA-RENAL)
Intra-renal failure typically involves direct injury to the kidney itself. The most common
cause is acute tubular necrosis (ATN). Some causes of ATN are ischemia, hypertension, nephrotoxin and some systemic vascular diseases such as lupus.
C.
POST-RENAL
In post-renal failure, the underlying cause is typically a bilateral obstruction below the level
of the renal pelvis and may be due to tumor development, thrombi, urinary tract
obstruction, or hyperthrophic prostate.
Notes:
Module 1: Lesson 2: Acute Renal Failure 21
PHASES OF ACUTE RENAL FAILURE
In most cases of acute renal failure, patients will progress through distinct phases as outlined
below.
• Oliguric phase
- Can last anywhere from five days to 21 days
- Low urine output (less than 400 mL/24 hrs)
- Protein in the urine
- Electrolyte imbalances
- Metabolic acidosis
•
Diuretic phase
- Begins when urine output begins to rise
- Has variable time frames, sometimes occurring
as little as 24 hours after the onset of renal failure
- Associated with potassium and sodium loss in
the urine
- Enhanced urine output may not reflect restored
kidney function but rather may be the result of
accumulating serum urea and creatinine, which
have an osmotic diuretic effect
• Recovery phase
- May last several months following the onset of the acute renal failure
- During this period, kidney function gradually returns to normal and proper urine
concentrations and volumes are achieved
Notes:
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Lesson 3: What is CRRT?
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Module 1: Lesson 3: What is CRRT?
25
CRRT: DEFINITION
Continuous renal replacement therapy (CRRT) is a
therapy indicated for continuous solute removal and/or
fluid removal in the critically ill patient. It allows for slow
and isotonic fluid removal that results in better
hemodynamic tolerance even in unstable patients with
shock and severe fluid overload. This process can be
applied to both adults and children.
CRRT can be modified at any time of the day and night
to allow adaptation to the rapidly changing
hemodynamic situation of critically ill patients.
CRRT therapy indications may be renal, non-renal, or a
combination of both. It is the treatment of choice for the
critically ill patient needing renal support and/or fluid
management.
HISTORY OF CRRT
‘The history of CRRT is relatively short. Its beginning was in 1977 when Kramer, while introducing a catheter into the femoral vein before hemodialysis, accidentally inserted the catheter into the
femoral artery. He realized the possibility of using the arteriovenous gradient for filtration of blood
and fluid elimination. He replaced the excessive losses by continuous infusion of substituting
solutions. He used for the method the term continuous arteriovenous hemofiltration (CAVH). This
was the first step in CRRT.’2 Over the past thirty years CRRT has continued to develop and has
emerged as a front line therapy for treatment of critically ill patients with acute renal failure.
Notes:
2
Hladik M, Tymonova J, Kadicik M, Adamkova M: Treatment by continuous renal replacement therapy in patients with burn
injuries. Burn Centre and Centre for Child Dialysis and Nephrology, University Hospital Ostrava, Czech Republic J. Tymonova
Burn Centre 17.listopadu 1790 708 52 Ostrava Czech Republic.
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Module 1: Lesson 3: What is CRRT?
CRRT GOALS3,4
• Removal of waste products
•
Restoration of acid-base balance
•
Correction of electrolyte abnormalities
•
Hemodynamic stabilization
•
Fluid balance
•
Nutritional support
•
Removal and/or modulation of septic mediators
CRRT INDICATIONS5
Accepted indications are acute renal failure combined with:
- Hemodynamic instability (cardiovascular)
- Severe fluid overload unresponsive to diuretics
- Hypercatabolic states/trauma - rhabdomyolysis
- High fluid requirements (nutrition, blood products)
Less established (non-renal) indications:
- Sepsis, lactic acidosis, acute respiratory distress syndrome (ARDS), multiple organ
dysfunction score (MODS)
- Chronic congestive heart failure (CHF), or decompensated CHF
- Pre- and post-cardiovascular surgery / coronary artery bypass graft (CABG)
- During extracorporeal membrane oxygenation (ECMO) for fluid management
Notes:
Bellomo R, Ronco C, Mehta R: Nomenclature for continuous renal replacement therapies. AJKA, Vol 28, No.5, pages S1-S7, November 1996.
Honore, et al: The big bang of hemofiltration: The beginning of a new era in the third millenium for extra-corporeal blood purification. IJAO/Vol29/
no 7, 2006/pp649-659.
5
Schetz, M: Non-Renal Indications for Continuous Renal Replacement Therapy. Kidney Intern Vol 53, Suppl 66 (1998).
3
4
Module 1: Lesson 3: What is CRRT?
27
PRINCIPLES OF CRRT / SOLUTE MANAGEMENT
DIFFUSION
Diffusion is the movement of solutes through a semi-permeable membrane from an area of higher
concentration to an area of lower concentration until equilibrium has been established.
•
The dialysate does not
mix with the blood
•
Efficient for removing
small molecules but not
large molecules
•
Molecular size and
membrane type can
affect clearances DIALYSATE
Diffusion occurs during
hemodialysis
NE
•
ME
MB
RA
Notes:
NE
In CRRT, diffusion
occurs when blood flows
on one side of the
membrane, and
dialysate solution flows
counter-current on the
other side
DIALYSATE
RA
•
BLOOD
MB
Solutes move from a
higher concentration to
a lower concentration
ME
•
Bicarbonate
Potassium
Urea
TNF
Blood cells
Bic
Pot
Ure
TNF
Blo
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Module 1: Lesson 3: What is CRRT?
CONVECTION
Convection is the one-way movement of solutes through a semi-permeable membrane with a
water flow. Sometimes it is referred to as solvent drag.
Efficient for both larger
and smaller molecules
•
The faster the substitution
flow rate, the higher the
clearance
•
Pressure difference
between the blood and
ultrafiltrate causes plasma water to be filtered
across. This causes
solvent drag for small and
large molecules across
the membrane leading to
removal from the blood.
The ultrafiltrate
containing the solute
should be replaced by
substitution solutions
DIALYSATE
BLOOD
FILTRATE
Substitution Fluid
MEMB
RAN
E
•
Bicarbonate
Potassium
Urea
TNF
Blood cells
Substitution solutions
must have near
physiological levels of
electrolytes and buffer,
and be sterile
•
Solute molecular size and membrane type can affect clearances
RA
Convection is a hemofiltration principle
ME
MB
•
NE
•
Notes:
Bicarbonate
Potassium
Urea
TNF
Blood cells
Module 1: Lesson 3: What is CRRT? 29
PRINCIPLES OF CRRT / FLUID MANAGEMENT
ULTRAFILTRATION
Ultrafiltration is the movement of fluid through a semi-permeable membrane along a pressure
gradient.
This gradient, positive to
negative, influences the
movement of fluid from
the blood side to the fluid
side, resulting in a net
removal of fluid from the
patient
•
The ultrafiltration rate
FILTRATE
depends on the pressure
applied to the filter, inside
and outside the fibers
•
Minimal solute
clearance happens by
convection during
ultrafiltration
RA
MB
ME
Notes:
NE
•
RA
Positive pressure is
generated on the blood
side of the membrane
and negative pressure is
generated on the fluid
side
FILTRATE
MB
•
BLOOD
ME
Positive and negative
pressures affect
ultrafiltration
NE
•
Water molecules
Blood cells
Positive pressure
Negative pressure
Wa
Blo
Po
Ne
30
Module 1: Lesson 3: What is CRRT?
ADSORPTION
Adsorption is the adherence of solutes and biological matter to the surface of a membrane.
High levels of adsorption can
cause certain filters to clog
and become ineffective
•
Membrane type affects
adsorptive tendencies
/effectiveness
•
Adsorption may also cause
limited removal of some
solutes (e.g., ß2
microglobulins) from the
blood
BLOOD
FILTRATE
MEMB
RAN
E
•
FILTRATE
Certain plasma proteins
Blood cells
In summary:
Principles used in all CRRT/blood purification therapies are:
MEMB
RAN
E
•
•
•
•
•
Diffusion (hemodialysis)
Convection (hemofiltration)
Diffusion & convection (hemodiafiltration)
Ultrafiltration (all therapies)
Adsorption (all therapies)
Notes:
Certain pla
Blood cells
Module 1: Lesson 3: What is CRRT? 31
CRRT/ Blood
Purification
SCUF
CVVHDF
CVVH
CVVHD
H E M O F I LT R AT I O N
H E M O D I A LYS I S
CONVECTION
DIFFUSION
CRRT includes several treatment modalities that use a veno-venous access. The choice will
depend on the needs of the patient and on the preference of the physician.
Slow Continuous UltraFiltration (SCUF)
Removal of ultrafiltrate at low rates without administration of a substitution solution. The purpose
is to prevent or treat volume overload when waste product removal or pH correction isn’t
necessary.
Continuous Veno-Venous Hemofiltration (CVVH)
Continuous convective removal of waste products (small and large molecules) utilizing a
substitution solution. pH is affected with the buffer contained in the substitution solution.
Continuous Veno-Venous HemoDialysis (CVVHD)
Continuous diffusive removal of waste products (small molecules) utilizing a dialysis solution. pH is
also affected with the buffer contained in the dialysate.
Continuous Veno-Venous HemoDiaFiltration (CVVHDF)
Continuous diffusive and convective removal of waste products (small and large molecules)
utilizing both dialysate and substitution solution. pH is also affected with the buffer contained in
the dialysate and substitution solution.
Notes:
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Module 1: Lesson 3: What is CRRT?
SLOW CONTINUOUS ULTRAFILTRATION6 (SCUF)
Primary therapeutic goal:
• Safe management of fluid removal
Primary indications:
• Fluid overload without significant electrolyte imbalance
Principle used: ultrafiltration
Therapy characteristics:
• No dialysate or substitution solutions
• Fluid removal only
NOTE: The colors of text in this Module indicate its correlation to elements of Figures 4-7
in the Operator’s Manual (p. 19-20)
Notes:
6
Operator’s Manual, Automated Fluid Balance Monitor, Aquarius for Platinum software version 6 U.S. Page 19.
Module 1: Lesson 3: What is CRRT? 33
CONTINUOUS VENO-VENOUS HEMOFILTRATION7 (CVVH)
Primary therapeutic goal:
• Solute removal and safe management of fluid volume
Primary indications:
• Uremia, severe acid/base or electrolyte imbalance
• When removal of larger molecular weight substances is required
Principle used: convection
Therapy characteristics:
• Requires substitution solution to drive convection
• No dialysate solution
• Effective at removing small and large molecules
Notes:
7
Operator’s Manual, Automated Fluid Balance Monitor, Aquarius for Platinum software version 6 U.S. Page 19.
34
Module 1: Lesson 3: What is CRRT?
CONTINUOUS VENO-VENOUS HEMODIALYSIS8 (CVVHD)
Primary therapeutic goal:
• Solute removal and safe management of fluid volume
Primary indications:
• Uremia, severe acid/base or electrolyte imbalance
Principle used: diffusion
Therapy characteristics:
• Requires dialysate solution to drive diffusion
• No substitution solution
• Effective at removing small to medium molecules
Notes:
8
Operator’s Manual, Automated Fluid Balance Monitor, Aquarius for Platinum software version 6 U.S. Page 20.
Module 1: Lesson 3: What is CRRT? 35
CONTINUOUS VENO-VENOUS HEMODIAFILTRATION9 (CVVHDF)
Primary therapeutic goal:
• Solute removal and safe management of fluid volume
Primary indications:
• Uremia, severe acid/base or electrolyte imbalance
• When removal of large molecular weight substances is required
Principle used: diffusion and convection
Therapy characteristics:
• Requires dialysate fluid and substitution solution to drive diffusion and convection
• Effective at removing small, medium and large molecules
Notes:
9
Operator’s Manual, Automated Fluid Balance Monitor, Aquarius for Platinum software version 6 U.S. Page 20.
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Lesson 4: Delivery of CRRT
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Module 1: Lesson 4: Delivery of CRRT
39
COMPONENTS OF A CRRT PROGRAM
•
Vascular access
•
Anticoagulation
•
CRRT system (machine, hemofilters,
line sets, accessories)
•
Fluid management
•
Team
VASCULAR ACCESS
NOTE: In this training guide, all references are to veno-venous vascular access. When
inserting vascular access for CRRT, please follow the manufacturer’s instructions and
your hospital’s protocols for insertion of central lines.
Vascular access is a basic prerequisite to perform any type of extracorporeal therapy. Access is
particularly important in CRRT where catheter performance is tested 24 hours a day. In dialysis
therapies, central venous catheters provide rapid and easy access permitting immediate use in
critically ill patients10. The most common catheter now in use is the large-bore, double-lumen
catheter. The primary sites for insertion include the femoral vein, internal jugular vein, and, less
commonly, the subclavian vein.
WARNING: To have an effective CRRT treatment, it is absolutely crucial to have functional
access. Failure to have functional access will result in a less than optimal treatment.
Using a blood pump, the patient’s blood is removed via the red coded line typically connected to
the red port of the catheter and delivered through the hemofilter back to the patient via the blue
coded line typically connected to the blue port.
Notes:
10
Ronco C, Bellomo R, LaGreca, (eds): Blood Purification in Intensive Care. Contrib Nephrol. Basel, Karger, vol 132, pp 266-282.
40
Module 1: Lesson 4: Delivery of CRRT
Many factors affect the functioning of a CRRT access11, 12, 13
•
Type and size of catheter
- Polyurethane or silicone
- French size
•
Length and placement site of catheter
To ensure proper flow, it is important that the appropriate catheter is placed in
the appropriate vessel. The following are suggestions.
- For jugular placement, it’s usually 12.5 cm on the right side and
15 cm on the left side (check each manufacturer’s
recommendations)
- For subclavian placement, it’s usually 15 cm on the right side and
20 cm on the left side (check each manufacturer’s recommendations)
- The femoral vein should have an extra long catheter (24 cm)
(check each manufacturer’s recommendations)
- Right side is anatomically easier to cannulate for jugular &
subclavian
- As a rule, the left side needs the longer catheter (Left-Long)
•
The patient’s disease processes and fluid status. (If the patient has hypercoagulopathies
and/or is dehydrated, it will be more difficult to maintain patency and proper flow)
Notes:
Canaud, et al.: Vascular access for extracorporeal renal replacement therapies in ICU. In: Ronco C, Bellomo R, LaGreca G, (eds):
Blood Purification in Intensive Care. Contrib Nephrol. Basel, Karger, vol 132, pp 266-282.
12
Kelber, et al.: Factors affecting delivery of high-efficiency dialysis using temporary vascular access. Am J Kidney Dis 1993;
22:24-9.
13
McGee WT, Ackerman BL, Rouben LR, Prasad VP, Bandi V, Mallory DL: Accurate placement of central venous catheters:
A prospective, randomized, multicenter trial. Crit Care Med 1993;21:1118-1123.
11
Module 1: Lesson 4: Delivery of CRRT
ANTICOAGULATION
Anticoagulants are used to prevent the blood
from clotting within the extracorporeal circuit
during the CRRT procedure. In many critically
ill patients undergoing CRRT, anticoagulation
is typically achieved through the use of lowdose heparin administered into the blood,
before the hemofilter. The remaining patients
may have underlying conditions, which put
them at high risk of bleeding, and therefore
heparin anticoagulation is not used.
All types of anticoagulation have risks. It is a
constant challenge to find a balance between
the risk of filter clotting and the risk of patient
bleeding.
The formation of clots in the blood is primarily the result of platelet activation and subsequent
obstruction of coagulation cascade. Therefore the majority of anticoagulation therapies are
designed to interfere with the coagulation pathway. Both the patient and the circuit should be
monitored to determine the effect of anticoagulation delivered, keeping in mind that preventing
patient bleeding takes priority over preventing filter clotting.
CRRT uses various anticoagulants, the most common of them are heparin and citrate.
WARNING: The use of citrate with CRRT is not FDA approved within the US.
Notes:
41
42
Module 1: Lesson 4: Delivery of CRRT
HEPARIN
Heparin is the most frequently used anticoagulant. It is commonly used during the priming of
the hemofilters and is infused into the CRRT circuit after the blood pump and before the filter.
The effects of heparin are systemic and both the patient and the CRRT circuit are anticoagulated.
All types of heparin carry the risk of heparin-induced thrombocytopenia (HIT) and platelet counts
must be monitored. If HIT is suspected, heparin must be discontinued immediately.
HEPARIN DELIVERY
•
Typical low-dose pre-filter heparin
- Approximately 5-10 units/kg/hr
- Delivered into the CRRT circuit post-pump, pre-filter
- Mildly elevates the activated partial thromboplastin time (aPTT)
•
Typical medium-dose pre-filter heparin
- Approximately 8-10 units/kg/hr
- Delivered into the CRRT circuit post-pump, pre-filter
- Mildly elevates the aPTT
•
Therapeutic systemic heparin
- Adjusted to achieve required aPTT as prescribed by physician
- Administered via a volumetric infusion pump
- Most commonly used for patients with systemic anticoagulation requirements, other than
CRRT needs
- Rarely used to prolong filter life
- If possible, infuse heparin pre-filter—however, remember to continue the infusion if
CRRT is stopped since its main indication is another need—i.e. deep vein thrombosis
(DVT), Atrial fibrillation, etc.
•
Regional heparin
- Rarely used
- Heparin is infused pre-filter and protamine infused post-filter to reverse effects of heparin
- Goal is to anticoagulate the circuit without anticoagulating the patient
Notes:
Module 1: Lesson 4: Delivery of CRRT 43
•
Low-molecular weight heparin
- Less likely to cause HIT
- Contra-indicated for patients who have developed HIT
- Difficult to monitor and difficult to reverse
- More expensive
WARNING: Precaution should be taken to monitor patient closely for excessive
anticoagulation due to heparin
OTHER ANTICOAGULANTS14, 15
Other, less frequently used anticoagulants mentioned in the literature, include:
•
•
•
•
Prostacyclin
Nafamostat mesilate
Hirudin
Agatroban
NO ANTICOAGULATION
In some circumstances, risks to the patient complicates
the use of any anticoagulant. These circumstances may
include, but are not limited to:
•
•
•
•
•
Active bleeding
Increased aPTT
Increased international normalized ratio (INR)
Liver failure
Low platelet count
Notes:
Davenport A: Anticoagulation in continuous renal replacement therapy. In: Ronco C, Bellomo R, LaGreca G (eds): Blood
Purification in Intensive Care. Contrib Nephrol, Basel, Karger, 2001, vol 132, pp 283-303.
15
Matsuo T, Kario K, Kodama K, Okamoto S: Clinical application of the synthetic thrombin inhibitor, Agatroban (MD-805) Semin
Thromb Hemost, 1992;18:155-60
14
44
Module 1: Lesson 4: Delivery of CRRT
THE CRRT SYSTEM
Delivering CRRT requires an integrated system consisting of:
•
Machine
•
Hemofilter
•
Line sets
•
Solutions
•
Accessories
CRRT MACHINE
The Aquarius is an instrument designed
to deliver CRRT. It consists of blood and
fluid pumps, user-friendly interface, scales
and integrated safeguards (see section
Getting Started with Aquarius of the
Operator’s Manual).
Notes:
Module 1: Lesson 4: Delivery of CRRT 45
HEMOFILTER
The hemofilter (often referred to as an artificial kidney)
is a requirement of any CRRT system. The hemofilter
contains a semi-permeable membrane in a hollowfiber design.
•
Blood flows inside of the hollow fibers
•
Dialysate flows on the outside of the fibers
•
Solute and fluid removal will be determined by the type of membrane and the surface area
(see Module 3 for available surfaces)
•
Hemofilters are usually synthetic
Semi-permeable membrane
Hollow fiber
Notes:
46
Module 1: Lesson 4: Delivery of CRRT
LINE SETS
The line set is used to transport blood and fluids through
the hemofilter and the CRRT circuit (see Module 3 for
detailed description)
ACCESSORIES
Other accessory products may be used in the
CRRT settings. They include:
•
Drainage bags
•
Three-way or four-way adaptor (manifold)
•
Stop cocks
•
Syringes
•
Anticoagulant
•
Priming solution
•
Dual-lumen catheters
Notes:
Module 1: Lesson 4: Delivery of CRRT 47
FLUID MANAGEMENT
The goals of fluid management in CRRT are typically to achieve two important functions:
•
Solute removal
•
Fluid removal
Substitution and dialysate solutions are used to facilitate
the removal of solutes from the patient’s blood using the
principles of convection (substitution) and/or diffusion
(dialysate). Fluids for this purpose are simultaneously
removed by the CRRT machine as delivered, and do not
affect the patient’s circulating volumes. Substitution
solutions can be infused before the filter (pre-dilution) and
after the filter (post-dilution).
To manage the patient’s circulating volume, it is often
necessary to remove fluid from the patient. This is Patient
Fluid Removal. When calculating Patient Fluid Removal, it
is necessary to consider the non-CRRT intakes and
outputs of the patient. Fluids removed from the patient
(substitution solutions and dialysate solutions) are
collected, as filtrate, in the drainage bag.
Notes:
48
Module 1: Lesson 4: Delivery of CRRT
SUBSTITUTION SOLUTION
•
•
•
•
•
•
•
•
•
•
Primary function: removal of solutes via convection (small,
medium, large)
Does not affect the patient’s intravascular volume
Must be physiological from an electrolyte standpoint and
sterile
They must be labeled for IV use
Can be pharmacy-prepared
Infused into the patient’s blood pre-dilution, post-dilution
or both
Formulation, volume, and infusion method (pre- or
post-dilution) are prescribed by a physician
Substitution solution allows convective clearance
The volume of substitution solutions infused is automatically removed by the machine
Sometimes referred to as ‘replacement fluid’
DIALYSATE SOLUTION
•
•
•
•
•
•
•
•
•
•
Primary function: removal of solutes via diffusion (small)
Does not affect the patient’s intravascular volume
Must be physiological and should be sterile
Commercially available (see Module 3 for codes and formulations available)
Prescribed by a physician
Dialysate solution allows diffusive clearance
Infused into the external dialysate port of the hemofilter counter-current to the blood flow
The volume of dialysate solutions infused is automatically removed by the machine
Buffers include lactate and bicarbonate (see Module 3 for codes and formulations available)
Formulation is usually calcium-free when used with citrate anticoagulation
WARNING: The use of citrate with CRRT is not FDA approved within the US.
Notes:
Module 1: Lesson 4: Delivery of CRRT 49
PATIENT FLUID REMOVAL
•
•
•
•
•
Fluid removed directly from the patient’s intravascular compartment
Hourly rate of removal is prescribed by the physician
Non-CRRT intakes and outputs must be calculated and considered
Fluid removal occurs by ultrafiltration
Fluid removed contains components of plasma water
FILTRATE
•
•
•
•
Filtrate is a combination of the substitution fluid, dialysate fluid and fluid removed from the
patient
Components of filtrate include water, electrolytes, waste products, immune mediators, drugs,
vitamins and amino acids
Filtrate is removed from the filtrate port of the hemofilter into a drainage bag
Filtrate is a biological waste substance, hospital protocols should be followed
TEAM
The addition of CRRT to the critically ill patient’s care requires the expertise, cooperation and
focus of a cross-functional team, which may include:
•
•
•
•
•
•
Notes:
Intensivist
Nephrologist
Critical care nurse
Nephrology nurse
Pharmacist
Dietician
50
Module 1: Lesson 4: Delivery of CRRT
SUMMARY
In summary, the main goals of CRRT are removal of waste products, restoration of acid/base
balance, and correction of fluid and electrolyte abnormalities, while maintaining hemodynamic
stability. The goal of any continuous renal replacement therapy is to replace, as best as possible,
the lost function of the native kidney. While CRRT provides a good option for a patient with ARF,
nothing will replace the complete function of a healthy kidney. The illustration below demonstrates
how the CRRT system attempts to mimic the function of the native kidney.
Renal artery = Access line
Renalartery
artery==
= Access
Access line
line
Renal
Renal
artery
Renal
artery
= Access
Access line
line
Renal vein = Return line
Renalvein
vein==
= Return
Return line
line
Renal
Renal
vein
Renal
vein
= Return
Return line
line
Kidney = Hemofilter
Kidney==
= Hemofilter
Hemofilter
Kidney
Kidney
Kidney
= Hemofilter
Hemofilter
Urether = Filtrate line
Urether==
= Filtrate
Filtrate line
line
Urether
Urether
Urether
= Filtrate
Filtrate line
line
Bladder = Drainage bag
Bladder==
= Drainage
Drainage bag
bag
Bladder
Bladder
Bladder
= Drainage
Drainage bag
bag
Notes:
Module 1: Lesson 4: Delivery of CRRT 51
Some studies16,17 suggest that recovery from acute renal failure is better when patients are treated
with CRRT. When normal kidney function can be restored, freedom from the need for chronic
dialysis can provide the patient with a better quality of life. The following illustration depicts kidney
function from a healthy kidney, to failure, to treatment, to recovery.
NORMAL KIDNEY
FUNCTION
RESTORED KIDNEY
FUNCTION
CRRT/ BLOOD PURIFICATION
INJURY/DISEASE
(SCUF/ CVVH/ CVVHD/ CVVHDF/ TPE)
ARF/ SEPSIS/ FLUID OVERLOAD
Notes:
Mehta RL, McDonald B, Gabbai FB, et al.: A Randomized clinical Trial of Continuous versus Intermittent dialysis for Acute Renal
Failure. Kidney Int 2001; 6: 1154-63.
17
Michael J. Jacka et al.: Continuous renal replacement therapy improves renal recovery from acute renal failure. Can J Anesth
2005; 52:3 pp 327- 332.
16
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Lesson 5: CRRT Considerations
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Module 1: Lesson 5: CRRT Considerations
57
ADVANTAGES
•
Compared to standard hemodialysis applied for a short period of time, CRRT provides
improved hemodynamic stability (slow, gentle and continuous)
•
Provides continuous fluid and electrolyte management (avoidance of rapid fluid and electrolyte
shifts)
•
May facilitate removal of cytokines and mediators18
•
Adapted to the needs of the critically ill
LIMITATIONS
•
Requires a large-bore central vascular access
•
Typically requires continuous anticoagulation
•
Requires immobilization of the patient for prolonged periods
Notes:
18
Bellomo, et al.: Extracorporeal blood purification therapy for sepsis and systemic inflammation: Its biological rationale. In: Ronco
C, Bellomo R, La Greca G (eds): Blood Purification in Intensive Care. Contrib Nephrol, Basel, Karger, 2001, vol 132, pp 367-374.
Module 1: Lesson 5: CRRT Considerations
58
SPECIAL CONSIDERATIONS
CRRT is used to treat critically ill patients, typically suffering from acute renal failure accompanied
by hemodynamic instability. While CRRT offers some advantages, certain parameters may require
special monitoring.
DRUG MANAGEMENT
Drug removal in CRRT techniques is dependent upon the molecular weight of the drug, the
sieving coefficient and the degree of protein binding. Drugs with significant protein binding are
removed minimally. Additionally, some drugs may be removed by adsorption to the membrane.
Most of the commonly used drugs require adjustments in dose to reflect the continuous removal
during CRRT19.
ACID/BASE AND ELECTROLYTE BALANCES
During CRRT, acid/base and electrolyte balances are continually modified, and should be
watched closely.
BLEEDING
Patients receiving continuous anticoagulation may be at risk of bleeding. The patient should be
monitored for bleeding. Patient’s clotting parameters and access site should be closely
monitored.
Notes:
19
Mehta RL: Supportive Therapies: Intermittent Hemodialysis, Continuous Renal Replacement Therapies, and Peritoneal Dialysis.
Atlas of Diseases of the Kidney (editor Schrier RW) Chapter 19, February 1999.
Module 1: Lesson 5: CRRT Considerations 59
HYPOTHERMIA20
CRRT patients are prone to hypothermia
due to the significant volume of blood
that is circulated outside of the body, and
the significant volumes of the substitution
and dialysate fluid used. During CRRT
significant thermal energy is lost. There
is little published on thermal energy exchange during CRRT, but some potential
effects of cooling could be:
•
•
•
•
May improve cardiovascular stability
May affect nutritional requirements
May affect immune function
May increase risk of circuit clotting
Warming both dialysate and substitution
fluids to 37º C (98.6º F) still leads to
thermal energy losses, and these losses
will be increased when larger volumes of
substitution and dialysate are used12.
Notes:
Davenport A: Dialysate and substitution fluids for patients treated by continuous forms of renal replacement therapy. In: Ronco
C, Bellomo R, La Greca G (eds): Blood Purification in Intensive Care, Contrib Nephrol, Basel, Karger, 2001, vol 132, pp 313-322.
20